The invention relates to a machine for washing and/or drying laundry that operates particularly on the front-loading principle, and to a method for determining and processing loading-relevant characteristic variables or, as the case may be, imbalance parameters of a laundry drum or drum shaft of the machine of the type indicated in the present invention.
A problem that arises while washing machines are operating is due to the vibrations occurring particularly during the spin phase. They result from the imbalance due to the laundry's uneven mass distribution in the laundry drum. Said imbalance may already exist from the time the washing process starts, but it can also first develop during a spin operation owing to different draining properties of the laundry and change over time as the process continues. Allowance will be made for the imbalance-induced forces by appropriately suspending the washing unit with the washing drum. The washing unit's suspension can still be overstrained, though, should a large imbalance occur at high revolution rates, which can cause the machine to what is termed walk or kick. But even when the machine is operating within tolerable vibration-induced excursion limits the imbalance-induced forces will lead not only to the development of undesired noise but also to greater wear-and-tear in the washing machine, particularly in its moving parts and bearings. Optimized washing-process controlling must hence be directed toward as comprehensive as possible determining of loading-relevant characteristic variables or, as the case may be, imbalance parameters and the evaluating thereof for effectively limiting and/or totally avoiding the imbalance due to the distribution of the laundry's mass.
Described as known in DE 100 22 609 C2 are a method for limiting the imbalance effect of a washing unit of a washing machine and a device for implementing said method. A plurality of sensors are therein attached in a distributed manner to the perimeter of a suds container of the washing machine for determining an imbalance occurring during the washing process due to a moving laundry drum. Said sensors register the imbalance-induced excursions of the suds container as well as the phase shifts between them. Measures to limit the imbalance will be initiated depending on the excursion values registered. Acceleration sensors or optical and/or electromechanical travel sensors can therein be employed as sensors.
What is to be seen as disadvantageous about that method and device is the fact that only the dynamic, already acting imbalance produced by the laundry's unbalanced loading can be detected by the sensors arranged on the suds container and, moreover, that not all parameters of relevance for effectively limiting said imbalance, such as, for instance, the total weight of the laundry in the washing drum, can be registered. What is further to be seen as disadvantageous is that on the one hand increased manufacturing costs will arise owing to the need for a plurality of sensors for implementing the method and that, on the other hand, attaching them to the perimeter of the suds container will impose structural-design limitations on the components also arranged in that region.